Hmm, I have the 2 prong PSU connector, so it seems like it's an earlier one, mine seems to have 11 2114 RAM ICs.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 15:52
by stephen_usher
OK, looking at what that's doing... One lead goes off to D2 on the VIC chip, with a NOR gate with something else, which is then flipped by the '04 and fed into the RAM /WE line.
So, I'm guessing that if a write is done to a specific address with D2 high then it doesn't get written to RAM. This suggests that whoever did this had a peripheral which sat somewhere and was controlled by a write to that address.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 15:57
by rubber_jonnie
stephen_usher wrote: 16 Feb 2022 15:52
OK, looking at what that's doing... One lead goes off to D2 on the VIC chip, with a NOR gate with something else, which is then flipped by the '04 and fed into the RAM /WE line.
So, I'm guessing that if a write is done to a specific address with D2 high then it doesn't get written to RAM. This suggests that whoever did this had a peripheral which sat somewhere and was controlled by a write to that address.
Sadly no peripherals that are obvious, or other internal mods. Interestingly, there is a wire that goes off to the CPU, pin 4 which is IRQ. Might try and fully reverse engineer the thing based on the wiring.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 16:25
by stephen_usher
Oh, that's the CPU, I thought it was the VIC chip.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 16:32
by rubber_jonnie
stephen_usher wrote: 16 Feb 2022 16:25
Oh, that's the CPU, I thought it was the VIC chip.
Yep, the VIC is in the 'boxed' area behind the video and IEC connector for the floppy.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 17:04
by BennehBoy
I can't believe how clean that VIC is, nice find.
You may find this interesting:
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 17:16
by rubber_jonnie
BennehBoy wrote: 16 Feb 2022 17:04
I can't believe how clean that VIC is, nice find.
You may find this interesting:
Yeah, I was a little shocked, it even still had the cardboard shielding inside :)
As for that vid, I watched it the other night :) Definitely a good bit of Commodore history.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 21:14
by rubber_jonnie
Well, I did something crazy tonight. I saved a program to cassette and loaded it back!!!
Here we are loading:
IMG_20220216_205757.jpg
And again after running my simple 2 liner:
IMG_20220216_205831.jpg
I already had the cassette deck with my C64, but it works a treat. Also came up lovely after a scrub with a magic sponge and a plastic wipe :)
Aren't the on screen letters HUUUUUUUUUUUGGGGGEEEE.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 21:44
by stephen_usher
Wow! Cassette loading? What will they think of next. Hehe.
Re: Whoops, I did it again! VIC-20 on the way...
Posted: 16 Feb 2022 21:51
by rubber_jonnie
stephen_usher wrote: 16 Feb 2022 21:44
Wow! Cassette loading? What will they think of next. Hehe.